1. Field of the Invention
The present invention relates to a fundus camera for use in taking a fundus image in group medical examination or the like, a control method for the fundus camera, and a program for executing the control method.
2. Description of the Related Art
In taking a fundus image of a subject by a general fundus camera, individual differences in light reflectance of the fundus need to be considered. Obtaining a uniform fundus image thus requires that the emission intensity of a light source be adjusted while observing the fundus. This method, however, takes time to perform photographing or photographing per subject, and is not suitable for group medical examination or other similar situations.
In light of the above, Japanese Patent Application Laid-Open No. 2003-116793 discloses a fundus camera having an automatic light intensity adjustment function, in which an appropriate emission intensity for photographing or photographing is calculated for light emission based on an observation light intensity, the gain of an image signal during observation, and the gain of an image signal during photographing.
Further, some fundus cameras can perform anterior ocular photographing to acquire an image of a peripheral part or iris of an eye to be inspected.
Japanese Patent Application Laid-Open No. H06-277184 discloses a fundus camera which uses an auxiliary lens to perform switching between a fundus mode and an anterior ocular mode.
A general fundus camera has an anterior ocular observation mode of observing the anterior ocular segment of the eye to be inspected in order to perform rough alignment to align a center part of the eye ball with an optical axis, and a fundus mode of observing the fundus portion of the eye to be inspected in order to perform alignment to adjust the eye ball position and the focus position more finely. Obtaining a good fundus image needs observation and adjustment of a photographing light intensity during the alignment. Light reflectance at the fundus portion is, however, different among persons, which needs manual adjustment of the light intensity for each photographing, thus leading to lengthening of inspection time.
In the technology disclosed in Japanese Patent Application Laid-Open No. 2003-116793, the emission intensity for photographing is calculated based on the light intensity and the image signal during observation. Accordingly, when an acquired image greatly changes, such as at the time of switching from anterior ocular observation to fundus observation, there is a large difference between the light intensity calculated for the anterior ocular observation and a necessary light intensity for fundus photographing. Therefore, calculation of the light intensity may take time.
Further, as described above, some fundus cameras, including the one disclosed in Japanese Patent Application Laid-Open No. H06-277184, have an anterior ocular photographing mode which enables photographing of the anterior ocular segment of the eye to be inspected.
In the anterior ocular photographing mode, in consideration of the burden on a subject and the influence on the pupil, a method of illumination with invisible near-infrared light is used in observation for performing alignment. However, in the case of using the automatic light intensity adjustment function which uses an image signal of an image of the anterior ocular segment irradiated with near-infrared light, an appropriate light intensity for photographing with visible light cannot be obtained because reflectance of the iris portion greatly differs between visible light and near-infrared light among racial groups.